Header catalog

Every header class exported from http_fields, grouped by function. All are frozen dataclasses sharing the same contract:

• Header.parse(value) — validate and parse a raw header value.

• direct construction from the header’s fields (scalars coerce; list headers take varargs).

• str(), bytes(), .value, .asgi_value for output.

• immutable, comparable, hashable.

A handful expose extra constructors — see Special constructors below.

Content negotiation

Header	Spec	Notes
Accept	RFC 9110	media ranges with weights
AcceptCharset	RFC 9110	charsets with weights
AcceptEncoding	RFC 9110	content codings with weights
AcceptLanguage	RFC 9110	language ranges with weights
AcceptRanges	RFC 9110	supported range units
Vary	RFC 9110	field names, or *

Representation metadata

Header	Spec	Notes
ContentType	RFC 9110	media type; builder ContentType.of(...)
ContentEncoding	RFC 9110	content codings
ContentLanguage	RFC 9110	language tags
ContentLength	RFC 9110	NonNegativeInt
ContentLocation	RFC 9110	a URI
ContentRange	RFC 9110	range unit + positions
ContentDisposition	RFC 6266	type + params; builder ContentDisposition.build(...)

Validators and conditionals

Header	Spec	Notes
ETag	RFC 9110	an entity-tag; builder ETag.from_tag(tag, weak=False)
LastModified	RFC 9110	a datetime
IfMatch / IfNoneMatch	RFC 9110	entity-tags, or * (wildcard=True)
IfModifiedSince / IfUnmodifiedSince	RFC 9110	a datetime
IfRange	RFC 9110	an EntityTag or datetime

Range requests

Header	Spec	Notes
Range	RFC 9110	range unit + IntRange / SuffixRange

Caching

Header	Spec	Notes
Age	RFC 9111	NonNegativeInt seconds
CacheControl	RFC 9111	cache directives
Expires	RFC 9111	a datetime

Authentication

Header	Spec	Notes
WWWAuthenticate / ProxyAuthenticate	RFC 9110	challenges
Authorization / ProxyAuthorization	RFC 9110	credentials
AuthenticationInfo / ProxyAuthenticationInfo	RFC 9110	auth-params

Cookies

Header	Spec	Notes
Cookie	RFC 6265	cookie pairs
SetCookie	RFC 6265	builder SetCookie.build(...); lenient SetCookie.parse(...)

Connection management

Header	Spec	Notes
Host	RFC 9110	hostname + optional port
Connection	RFC 9110	connection options
Upgrade	RFC 9110	protocols
Via	RFC 9110	intermediaries
Trailer	RFC 9110	field names
TE	RFC 9110	transfer codings with weights
MaxForwards	RFC 9110	NonNegativeInt

Request context

Header	Spec	Notes
From	RFC 9110	a mailbox
Referer	RFC 9110	a URI
UserAgent	RFC 9110	products / comments
Expect	RFC 9110	expectations (usually 100-continue)

Response context

Header	Spec	Notes
Allow	RFC 9110	methods
Date	RFC 9110	a datetime
Location	RFC 9110	a URI
RetryAfter	RFC 9110	NonNegativeInt or datetime
Server	RFC 9110	products / comments

CORS / Fetch

Header	Spec	Notes
Origin	RFC 6454 / Fetch	an origin
AccessControlAllowOrigin	Fetch	origin, null, or *
AccessControlAllowCredentials	Fetch	always true
AccessControlAllowMethods	Fetch	methods
AccessControlAllowHeaders / AccessControlExposeHeaders / AccessControlRequestHeaders	Fetch	field names
AccessControlMaxAge	Fetch	NonNegativeInt
AccessControlRequestMethod	Fetch	a single method

Other extensions

Header	Spec	Notes
Forwarded	RFC 7239	forwarding elements
Link	RFC 8288	link values
StrictTransportSecurity	RFC 6797	max_age + include_subdomains / preload
AltSvc / AltUsed	RFC 7838	alternative services (clear=True for clear)
Prefer / PreferenceApplied	RFC 7240	preferences

Structured Fields (RFC 9651)

See also Work with Structured Fields.

Header	Spec	Notes
Priority	RFC 9218	urgency (0-7) + incremental
CacheStatus	RFC 9211	SF List of cache entries
ProxyStatus	RFC 9209	SF List of intermediaries
ContentDigest / ReprDigest	RFC 9530	SF Dictionary of algorithm → digest

Generic

Header	Notes
CustomHeader	any header with an arbitrary field name; CustomHeader(name, value)

Special constructors

Beyond .parse() and direct construction:

Header	Constructor
ContentType	ContentType.of(type, subtype, *, charset=None, boundary=None, params=None)
SetCookie	SetCookie.build(cookie_name, cookie_value, *, domain=None, path=None, expires=None, max_age=None, secure=False, http_only=False, samesite="Lax", extension=None)
ContentDisposition	ContentDisposition.build(disposition_type, disposition_parms=None)
ETag	ETag.from_tag(tag, weak=False)
IfMatch, IfNoneMatch	IfMatch(*entity_tags, wildcard=False)
AltSvc	AltSvc(*values, clear=False)